End stage renal disease (ESRD) is an important public health issue. Based on 2005 USRDS data ESRD patients utilize 19.2 percent of medicare spending (21.3 billion dollars). Diabetic nephropathy and glomerulonephritis contributes about 56.5 percent of the incident patients on dialysis. Glomerulus is the filtering unit of the kidney. Podocytes are morphologically unique cells, which have octopus-like processes (foot processes) which interdigitate to form the slit diaphragm. Most glomerular diseases present with proteinuria and podocyte foot process effacement. Our lab has identified signaling mechanisms employed by slit diaphragm proteins to regulate the actin cytoskeleton of the podocyte. These signaling mechanisms appear to be essential for maintaining the unique structure and function of this cell. Human mutations of several of these gene products such as Nephrin, Podocin, and alpha actinin-4 lead to foot process effacement and proteinuria and result in scarring of the kidney causing renal failure and eventually end stage renal disease requiring dialysis. The guiding hypothesis of this application is that the slit diaphragm protein complex regulates podocyte actin cytoskeletal dynamics. Based on our preliminary work, this project will focus on several aspects of this mechanism. Specifically we will: (1) Investigate signaling mechanisms by which Nephrin and Neph1 cooperate in actin polymerization. Our preliminary data suggests a role for nWASP and cortactin in Nephrin/Neph1 mediated actin polymerization. These proteins are known to assemble, promote, regulate and stabilize the actin polymerization complex. Using biochemical and cell biological techniques we will characterize the interaction of these two proteins with Nephrin and Neph1. (2) Investigate the role of cofilin in podocyte actin cytoskeletal dynamics. Our preliminary data shows a signaling relationship between Nephrin and cofilin. Cofilin is necessary for actin polymerization and remodeling. 3. To further characterize the physiological role of cofilin in podocytes in development and in podocyte injury, we will engineer and phenotye mice deleted of cofilin in a podocyte-specific fashion.